1. Field of the Invention
The present invention relates to a communication node and a switching device used in the communication node, and more particularly to the communication node making up a large-capacity and high-speed optical network and having a signal protection function for an optical signal communication line in the high-speed optical network, and the switching device used in the communication node.
The present application claims priority of Japanese Patent Application No. 2002-209776 filed on Jul. 18, 2002, which is hereby incorporated by reference.
2. Description of the Related Art
Conventionally, in a large-capacity and high-speed optical network, a direction of a signal that can be transmitted by one piece of an optical fiber transmission line is only one direction.
When bidirectional signals of an upward signal and a downward signal are to be transmitted between communication devices facing each other, two pieces of optical fiber communication lines are required.
Moreover, in order to provide signal protection against a failure in an optical fiber communication line, two pieces of optical fiber communication lines, one serving as an optical fiber transmission line being presently activated and another serving as an optical fiber transmission line being prepared for standby use for each of the upward and downward signals. Therefore, in this case, four pieces of optical fiber transmission lines are required.
An example of a conventional optical network having a function of signal protection is disclosed in Japanese Patent Application Laid-open No. Hei 4-334135. In the disclosed conventional optical network, an optical signal transmitted from the optical signal transmitting device is branched by an optical directional coupler into two signals, one flowing through an optical fiber transmission line being presently activated and another flowing through an optical fiber transmission line being prepared for standby use. Each of optical signals transmitted through the two optical fiber transmission lines is received separately by one of two optical signal receiving devices. Then, a signal switching switch selects either of the signals received by the two optical signal receiving devices.
Bidirectional optical transmission including upward and downward transmission can be achieved by combining two configurations disclosed in the above Japanese Patent Application Laid-open No. Hei 4-334135.
Moreover, in Japanese Patent Application Laid-open No. Hei 10-336120, an example of configurations of a conventional optical network is shown in which bidirectional transmission that can provide signal protection is achieved by using two pieces of optical fiber transmission lines. In the disclosed configuration, two nodes are placed so as to face each other, which are connected by two optical fiber transmission lines (being called “bidirectional lines” in the above Patent Application). Each of the nodes has a switching unit and an optical unit. The switching unit is used to handle electrical signals which operates to switch connection of signals to do switching for signal protection. The optical unit is made up of an optical signal transmitting device and an optical signal receiving device which operate to convert an electrical signal to an optical signal and vice versa in order to transmit and receive an optical signal.
In the optical network disclosed in Japanese Patent Application Laid-open No. Hei 10-336120, an upward signal for present operations and a downward signal for standby operations are transmitted by a first optical fiber transmission line and a downward signal for present operations and an upward signal for standby operations are transmitted by a second optical fiber transmission line.
In the above example, let it be assumed, for example, that a failure occurs in the first optical fiber transmission line. Since the upward signal for present operations is being transmitted through the first optical fiber transmission line, switching is done so that the upward signal is transmitted through the second optical fiber transmission line provided for standby use. The switching for signal protection is done electrically within the switching unit.
When bidirectional optical transmission is to be achieved by combining two configurations disclosed in the above Japanese Patent Application Laid-open No. Hei 4-334135, an optical fiber transmission line being presently activated and an optical fiber to be prepared for standby use are required for each of an upward signal and downward signal. That is, four optical fiber transmission lines are required.
Therefore, in the optical network disclosed in Japanese Patent Application Laid-open No. Hei 4-334135, many optical fiber transmission lines have to be installed, thus causing increased costs for the installation of the optical network. Moreover, in the case of providing service using a dark fiber, its usage charge is costly.
Also, in the optical network disclosed in Japanese Patent Application Laid-open No. Hei 4-334135, four pieces of optical signal receiving devices are required, one for receiving an upward signal for present operations, another for receiving an downward signal for present operations, a third for receiving an upward signal for standby operations, and a fourth for receiving a downward signal for standby operations. Furthermore, when an optical signal transmitting device has to be constructed so that optical signal transmission is carried out in a duplexed manner to achieve improvement of reliability, four pieces of optical signal transmitting devices, as in the case of the optical signal receiving device, are required accordingly.
Therefore, in the conventional optical network disclosed in Japanese Patent Application Laid-open No. Hei 4-334135, increased costs for the optical transmission device are inevitable due to the many required optical components. An optical signal transmitting device and an optical signal receiving device that can provide a transmission speed exceeding 10 G bps, in particular, are very costly and large in size, which causes high costs for the optical transmission device.
Moreover, since components prepared for standby use including the optical fiber transmission line, the optical signal transmitting device, and the optical signal receiving device are not utilized in normal times, a transmission band that the network system can use is not effectively used.
Also, in the optical network disclosed in Japanese Patent Application Laid-open No. Hei 10-336120, the optical unit requires four pieces of optical signal transmitting devices including the optical signal transmitting device being presently activated to transmit the upward signal, the optical signal transmitting device being presently activated to transmit the downward signal, the optical signal transmitting devices being prepared for standby use to transmit the upward signal and the optical signal transmitting device being prepared for standby use to transmit the downward signal. Similarly, the optical unit requires four pieces of optical signal receiving devices including the optical signal receiving device being presently activated to receive the upward signal, the optical signal receiving device being presently activated to receive the downward signal, the optical signal receiving device being prepared for standby use to receive the upward signal and the optical signal receiving device being prepared for standby use to receive the downward signal.
As a result, in the optical network disclosed in Japanese Patent Application Laid-open No. Hei 10-336120, as in the case of that disclosed in Japanese Patent Application Laid-open No. Hei 4-334135, increased costs of the optical transmission device is inevitable due to the many required optical components. Also, an optical signal transmitting device and an optical signal receiving device that can provide a transmission speed exceeding 10 G bps, in particular, are very costly and large in size, which causes high costs for the optical transmission device.